1. Field of the Invention
This invention relates to an image pickup apparatus.
2. Description of the Related Art
In a single-plate color video camera apparatus, in order to obtain color information from an image of a single image pickup device, color filters are arranged on a photosensitive surface in the form of a mosaic. Mg, Ye, Cy and G complementary-color mosaic filters, which are now most frequently used, are arranged as shown in FIG. 6(a) which shows pixel arrangement of complementary-color mosaic filters. A value corresponding to the spectral sensitivity characteristics of each complementary filter is obtained as an output from the image pickup device. When the camera is used as a movie camera for obtaining moving images, in order to conform to interlaced scanning standards, such as the NTSC or the like, signals obtained by adding pixel signals on the n-th line and the (n+1)-th line, on the (n+2)-th line and the (n+3)-th line, . . . are used for even fields, and signals obtained by adding pixel signals on the (n-1)-th line and the n-th line, on the (n+1)-th line and (n+2)-th line, . . . are used for odd fields. Accordingly, signals as shown in FIG. 6(b) which shows an output of an image pickup device are obtained as output signals from the image pickup device. In FIG. 6(b), Wr=Mg+Ye, Wb=Mg+Cy, Gr=G+Ye, and Gb=G+Cy. By performing interpolation by adjusting the spatial phases of respective Wr, Wb, Gr and Gb complementary-color signals, respective Wr, Wb, Gr and Gb complementary-color signals for one frame are generated. For example, as for Wr, when the output of the image pickup device is Wr, the Wr signal is used as it is. When the output of the image pickup device is other than Wr, the average of Wr's spatially adjacent to the target pixel (Wr's immediately before and after the target pixel, or Wr's on lines in the same field immediately before and after the line on which the target pixel is present, or Wr's in four oblique directions) is calculated to generate a Wr signal. Since the sampling frequency for each complementary-color signal is 1/2 of the pixel sampling frequency fs of the image pickup device, the band of the sampling frequency is limited so as to suppress folded components generated from a signal having a frequency of fs/2. By performing matrix calculation for complementary-color signals generated in the above-described manner, R, G and B three-primary-color signals are generated.
In the above-described conventional approach, theoretically, when separating/generating each complementary-color signal from the output of the image pickup device, carriers and folded components are generated as pseudocolor signals in vertical, horizontal and oblique directions for every frequency equal to 1/2 of the pixel sampling frequency fs by the image pickup device, thereby causing deterioration in the picture quality. In order to remove the above-described folded components, theoretically, each complementary-color signal must be separated/generated after limiting the band of the output signal of the image pickup device before separating/generating the complementary-color signal to 1/4 of the pixel sampling frequency in vertical, horizontal and oblique directions. However, this approach cannot be adopted because a color modulation component is superposed in the output signal of the image pickup device.
Conventionally, in order to solve the above-described problems, in addition to the above-described R, G and B three-primary-color signals, signals obtained by removing the color modulation component included in the output of the image pickup device by an LPF (low-pass filter) are generated (if spectral sensitivity characteristics of complementary-color filters are ideal, the signals equal R+1.5 G+B, and the band can be allowed up to 1/2 of the pixel sampling frequency). By performing matrix calculation between the generated signals and the R, G and B three-primary-color signals, R, G and B three-primary-color signals having a wide band are generated. However, while the the wide-band R, G and B three-primary-color signals provide a finer image than an image provided by the original R, G and B three-primary-color signals, accuracy in colors is reduced, so that a whity image is obtained.